Why was Africa so vulnerable to the slave trade? Because of West and Central Africa's political fragmentation. Many of the region's larger political units--such as Ghana and Mali--had declined, and the absence of strong, stable political units made it more difficult to resist the slave trade.

In retrospect, it seems clear that the Atlantic slave trade depended upon a highly complex set of variables. Trade winds and ocean currents needed to make it easy to sail from the western African coast to Brazil and the Caribbean. Africa needed to have a high birth rate. It is an unsettling historical irony that crops from the new World--such as cassava, squash, and peanuts--stimulated population growth in Africa. Rapid population growth, in turn, made the slave trade possible.